Baldturbofreak
05-18-2010, 11:13 PM
Some folks have been almost upset when they make the initial pull on our Dynomite.
Here is a clip from the recent news letter from land and sea that might shed some light on why your dynosheet doesnt show what you think it "should".
Question of the Month...?
“Our dyno reads low! I know the engines/cars that we build make
more power than this dyno reports. You can even hear and feel
how much harder it is pulling than the data shows. We ‘tweaked’
our calibration to get readings equal to other shops. What is
wrong with this dyno?”
We have touched on this before. So, many of you already know
where this is heading. In the majority of these cases, the “low”
dynamometer is correct! That engine is just not outputting the
power levels the owner and/or engine builder wishes [COLOR=#231f20]it were.
However, wishing does not automatically make it so. Neither do
observers’ “ feelings ,” about noise and vibration, trump calibrated
instruments – not when it comes to measuring torque and power.
The biggest trap of them all is the conclusion that: “...my engine
must be making more power (than this dynamometer shows),
because all the other dyno results I hear about are so much higher.”
Even if you knew for certain that those other dyno results were true
(almost never the case) that still does not endow your engines with
matching (or better) performance.
Too often, however, almost everyone begins to believe everyone
else’s exaggerations (a.k.a. lies). Repeating someone’s exaggeration
(or outright fabrication), even over and over, does not eventually
make it true.
Sometimes an engine builder’s rationalization goes something like
this: if product X, Y, and Z all claim to add 20% more power – I
will be conservative and assume they each add only about 5% more
power. Therefore, my creation must be making (at least) 15% more.
Another variation: those guys have a dyno report that shows 600
horsepower. My car beat theirs. So, my engine must make even
more than 600 Hp!
Even shop owners that know something is not right often cave in to
all of this. Their excuse: “...I had to increase the numbers we were
reporting, to be competitive with the other tunning shops.”
A dyno should be treated like any other measurement tool. It has to
calibrated against verifiable standards. Measuring power from a
running engine requires knowing its delivered torque and rate of
delivery. The formula (definition) for English horsepower = torque
x RPM / 5252.1131 (using foot-pounds for torque). Most tuners
recognize that the tachometer is accurate, so the argument typically
only involves the dynamometer’s torque calibration. Fortunately,
like any scale, load-cell accuracy is easily verifiable via deadweight
testing – using certified weights.
Additionally, most absorber-equipped dynamometers can separately
plot inertial energy (stored in the system’s rotating components)
from steady-state power (absorbed via the dyno’s brake). Because
inertial readings do not require any load-cell measurements (only
accurate component measurements and delta-RPM readings) they
are available for double-checking against your load cell power data.
When the two agree, the dyno is right! This is all that the engine is
producing. Maybe it is due to the test cell’s ventilation conditions,
or some other non-engine problem, but that is another matter – your
dynamometer’s low numbers are still correct!
Here is a clip from the recent news letter from land and sea that might shed some light on why your dynosheet doesnt show what you think it "should".
Question of the Month...?
“Our dyno reads low! I know the engines/cars that we build make
more power than this dyno reports. You can even hear and feel
how much harder it is pulling than the data shows. We ‘tweaked’
our calibration to get readings equal to other shops. What is
wrong with this dyno?”
We have touched on this before. So, many of you already know
where this is heading. In the majority of these cases, the “low”
dynamometer is correct! That engine is just not outputting the
power levels the owner and/or engine builder wishes [COLOR=#231f20]it were.
However, wishing does not automatically make it so. Neither do
observers’ “ feelings ,” about noise and vibration, trump calibrated
instruments – not when it comes to measuring torque and power.
The biggest trap of them all is the conclusion that: “...my engine
must be making more power (than this dynamometer shows),
because all the other dyno results I hear about are so much higher.”
Even if you knew for certain that those other dyno results were true
(almost never the case) that still does not endow your engines with
matching (or better) performance.
Too often, however, almost everyone begins to believe everyone
else’s exaggerations (a.k.a. lies). Repeating someone’s exaggeration
(or outright fabrication), even over and over, does not eventually
make it true.
Sometimes an engine builder’s rationalization goes something like
this: if product X, Y, and Z all claim to add 20% more power – I
will be conservative and assume they each add only about 5% more
power. Therefore, my creation must be making (at least) 15% more.
Another variation: those guys have a dyno report that shows 600
horsepower. My car beat theirs. So, my engine must make even
more than 600 Hp!
Even shop owners that know something is not right often cave in to
all of this. Their excuse: “...I had to increase the numbers we were
reporting, to be competitive with the other tunning shops.”
A dyno should be treated like any other measurement tool. It has to
calibrated against verifiable standards. Measuring power from a
running engine requires knowing its delivered torque and rate of
delivery. The formula (definition) for English horsepower = torque
x RPM / 5252.1131 (using foot-pounds for torque). Most tuners
recognize that the tachometer is accurate, so the argument typically
only involves the dynamometer’s torque calibration. Fortunately,
like any scale, load-cell accuracy is easily verifiable via deadweight
testing – using certified weights.
Additionally, most absorber-equipped dynamometers can separately
plot inertial energy (stored in the system’s rotating components)
from steady-state power (absorbed via the dyno’s brake). Because
inertial readings do not require any load-cell measurements (only
accurate component measurements and delta-RPM readings) they
are available for double-checking against your load cell power data.
When the two agree, the dyno is right! This is all that the engine is
producing. Maybe it is due to the test cell’s ventilation conditions,
or some other non-engine problem, but that is another matter – your
dynamometer’s low numbers are still correct!